1. Field of the Invention
The present invention relates to a technique for manufacturing a semiconductor device. More specifically, the present invention concerns a technique effectively applicable to lithography using a photomask (hereafter simply referred to as a mask) during a semiconductor device manufacturing process.
2. Prior Art
In semiconductor device manufacturing, lithography is used as a method of forming a fine pattern on semiconductor wafers. The mainstream lithography is the so-called optical projection exposure method which repeatedly prints a mask-formed pattern on semiconductor wafers via the reduction projection optics. The basic configuration of a stepper is described in, for example, Japanese Patent Application Laid-Open Publication No. 2000-91192.
Generally, resolution, R, on a semiconductor wafer according to the projection exposure method is expressed as R=kxc3x97xcex/NA. In this formula, k is a constant dependent on a resist material or a process; xcex is an illumination light wavelength; and an NA is a numerical aperture for a projection exposure lens. As seen from this formula, a finer pattern is necessary when using the projection exposure technique, using a light source with a shorter wavelength. Presently, the semiconductor device manufacture uses a stepper whose illumination light source is a mercury lamp""s i-line (xcex=365 nm) or a KrF excimer laser (xcex=248 nm). Further fining patterns require a light source with a shorter wavelength, making the use of ArF excimer laser (xcex=193 nm) or F2 excimer laser (xcex=157 nm) under consideration.
An ordinary mask used for this type of lithography is fabricated by processing a transparent mask plate. On this plate, there is formed an opaque metal layer such as chromium (Cr) and the like, or a dimming or opaque inorganic film such as MoSi, ZrSiO, SiN, and the like. An ordinary mask comprises the above-mentioned transparent mask plate on which the above-mentioned metal or inorganic film with a specified shape is formed. However, the thus configured mask causes problems; it requires many manufacturing processes, involves increasing costs, and decreases processing accuracy. The reason is that an opaque pattern is processed with isotropic etching. Considering these problems, Japanese Patent Application Laid-Open Publication No. 5-289307 discloses the technique of using a resist layer for an opaque pattern on the mask plate. This technique is based on the characteristic that the ArF excimer laser decreases transparency of a specified resist layer.
However, the inventors found that the technique of using the resist layer for an opaque pattern is subject to the following problems.
First, an opaque pattern comprising the resist layer cannot sufficiently shield the light with a wavelength over 200 nm. Generally, the exposure light such as KrF excimer laser (xcex=248 nm) or i-line (xcex=365 nm) is used for manufacturing a volume zone on a semiconductor integrated circuit device. An applicable wavelength for the resist layer is critical for the opaque pattern formation.
Second, no sufficient consideration is given about more efficiently manufacturing masks in a short period. In recent years, reflecting a trend of system LSI (Large Scale Integrated) circuits, there is an increasing need for developing and manufacturing a small quantity of, and many types of LSI chip in a short period. The manufacture of these LSI chips uses, for example, 20 to 40 masks. The TAT (turn-around time) for manufacturing masks is a driving force for the LSI development competition. As an advanced feature is requested for this type of LSI chips, the product development requires more processes and a longer period. By contrast, the existing product becomes obsolete soon and the product life is short. It is expected to shorten a period for the product development and manufacture. Especially, a system LSI chip is subject to a high debug ratio for the wire layer. It is important to supply masks for wire layer in a short period and at a low cost for shortening a period and reducing costs for the LSI development. Accordingly, a significant problem is how to efficiently manufacture masks used for this product manufacture in a short time.
Third, no sufficient consideration is given concerning reduction of mask costs. Elements and wires are further fined along with a request to increase integration of elements in a semiconductor integrated circuit device and to increase an operation speed. In addition, strict accuracy is requested for processing mask patterns. An increase in the amount of pattern data remarkably increases mask production costs. Generally, as mentioned above, a plurality of masks is used for one type of semiconductor integrated circuit device. An increase in mask production costs is a serious problem. The technological development progresses with the intention of shortening the exposure light wavelength along with fining of elements and wires. However, shortening the wavelength requires rare and precious lens materials such as CaF2 and the like. Moreover, optical members are subject to great irradiation damage, shortening the parts life. Hence, the short-wavelength exposure is expensive. When the exposure process for semiconductor integrated circuit devices simply uses a mask having the opaque pattern comprising the above-mentioned resist layer, the ArF excimer laser exposure needs to be used in many cases. Consequently, though the mask cost decreases, the total production cost rather increases.
It is an object of the present invention to provide a technique capable of efficiently printing a specified pattern even if the exposure process using a resist mask uses exposure light with a wavelength over 200 nm.
It is another object of the present invention to provide a technique capable of shortening a period for developing semiconductor devices.
It is still another object of the present invention to provide a technique capable of shortening a period for manufacturing semiconductor devices.
It is yet another object of the present invention to provide a technique capable of decreasing semiconductor device costs.
These and other objects and new features will become more apparent as the description in this specification proceeds when considered in connection with the accompanying drawings.
The following summarizes representative inventions disclosed in this specification.
Namely, the present invention comprises a process of printing a specified pattern on a semiconductor wafer by exposing the semiconductor wafer through the use of a photomask provided with an opaque pattern comprising a photoabsorptive organic layer in reaction to exposure light with a wavelength over 200 nm.
Further, according to the present invention, the organic layer comprises a photosensitive organic layer formed on a photoabsorptive organic layer in reaction to exposure light with a wavelength over 200 nm.
Moreover, the present invention selectively uses a photomask provided with an opaque pattern comprising a first photoabsorptive organic layer in reaction to exposure light with the wavelength of 200 nm or shorter and a photomask provided with an opaque pattern comprising a second photoabsorptive organic layer in reaction to exposure light with a wavelength over 200 nm according to a pattern to be exposed.
Furthermore, according to the present invention, the first organic layer is a photoabsorptive photosensitive organic layer reactive to exposure light with the wavelength of 200 nm or shorter. The second organic layer comprises a photosensitive organic layer formed on the photoabsorptive organic layer reactive to exposure light with a wavelength over 200 nm.
Still further, the present invention selectively uses a photomask provided with an opaque pattern comprising a metal layer and a photomask provided with an opaque pattern comprising a photosensitive organic layer formed on the photoabsorptive organic layer reactive to exposure light with a wavelength over 200 nm, according to a pattern to be exposed.